In electronics industry, needs for a greater packing density and speedup are ever more increasing in the production technology of the IC field. In silicon ULSI, and in particular, in the logic ULSI, the current challenge resides not so much in the improvement of the performance by using a finer design rules in MOSFET but rather, in the improvement of the performance of the interconnect connecting the MOSFET. More specifically, decrease in the interconnect resistance and decrease in the inter-wiring and interlayer capacities are required in solving the problem of interconnect delay associated with the multilayer interconnection.
In view of such situation, replacement of the aluminum interconnect which is currently used in most integrated circuits with a copper interconnect has become inevitable since the copper interconnect has a lower electric resistance and a higher migration resistance. Under such situation, a process comprising the step of forming seeds by sputtering followed by copper plating has become a commercially practical method.
Various proposals have been made for the interlayer insulator film material with low dielectric constant for use in reducing the inter-wiring and interlayer capacities, and examples of the conventional inorganic materials include silicon dioxide (SiO2), silicon nitride, and phosphosilicate glass, while exemplary conventional organic materials include polyimide. In order to form a more consistent interlayer insulator film, one recent proposal uses SiO2 produced by hydrolysis, namely, polycondensation of tetraethoxysilane monomer as a coating material for “spin on glass” (inorganic SOG). Also proposed is use of a polysiloxane obtained by polycondensation of an organic alkoxysilane monomer for the organic SOG.
Two categories of film formation methods are used in the formation of the insulator film. One is the coating method in which the solution of the polymer for the insulator film is coated by spin coating to form the insulator film, and the other is chemical vapor deposition (CVD), the typical method being plasma enhanced chemical vapor deposition (hereinafter also abbreviated as plasma CVD or PECVD) in which the source material is excited in plasma for reaction and film formation.
With regard to the plasma CVD, JP-A 2002-110670 proposes use of the plasma CVD for depositing a thin film of trimethylsilane oxide from trimethylsilane and oxygen, and JP-A 11-288931 proposes deposition by the plasma CVD of a thin film of an alkylsilane oxide from an alkoxy silane having a straight chain alkyl such as methyl, ethyl, or n-propyl, an alkenyl such as vinyl, or an aryl such as phenyl.
In order to further reduce the dielectric constant in the Si-containing film formed by plasma CVD, WO 2005/53009 proposes a method using a silane compound having a radically polymerizable organic group on its side chain in which a Si-containing film is formed by polymerizing the polymerizable organic group under the CVD conditions, and USSN 2005/0194619 proposes a method using a silane in which the silicon atoms are connected by an intervening hydrocarbon group.
However, the film which has been designed to have a higher porosity for the sake of the reduced dielectric constant suffers from the processing damage during the subsequent etching, ashing and washing steps.
For example, a film having a low dielectric constant with well-conserved side chains can be formed from the material proposed in WO 2005/53009. This film, however, suffers from unstable physical properties due to the processing damage in the subsequent steps due to the unsaturated bonds remaining in the film.
The material having a high porosity also suffers from increased risk of the damage when it is treated by an alkaline solution. This damage starts from hydrophilization of the insulator film surface, and nucleophilic attack on the Si having Si—O bond results in the increase of the dielectric constant of the film.
The likeliness of the nucleophilic attack on the silicon atom is highly affected by polarization of the silicon atom by the substituent. More specifically, most silicon atoms in the film should have 3 or 4 bonds to constitute the three dimensional structure, and as described above, these bonds are usually bonds by intervening oxygen atom. The oxygen atom bonded to the silicon atom, however, increases reactivity of the silicon atom for the nucleophilic reaction by its polalization effect.
In the meanwhile, a film obtained by using a silane in which the silicon atoms are connected by an intervening hydrocarbon group for the source material is proposed in USSN 2005/0194619. This film can be deemed as a film in which the bonding of the silicon atoms by the oxygen atom for constituting skeletal structure which is necessary for forming the porous film has been partly substituted by the hydrocarbon group. This in turn mean that, when this method is used, the skeletal structure can be formed even if the ratio of the total number of oxygen atoms to the total number of silicon atoms in the film in bulk state is reduced.
Alternatively, the nucleophilic attack on the silicon atom may be suppressed by increasing the hydrophobicity of the film. In this method, intrusion of the nucleophilic species into the film is prevented by adding an alkyl substituent to the silicon atom to thereby increase hydrophobicity of the film.
However, when a silane in which the silicon atoms are connected by an intervening hydrocarbon group or a silane in which substantial number of hydrophobic substituents are present on the silicon atom is used for the starting material, the vapor pressure of the silane will be reduced. As a consequence, when a silicon-containing film is formed by using such silane, the film deposition speed will be reduced compared to the conventional film formation.